A sintered body of zirconia obtained by sintering zirconia powder has been used as ceramics for various kinds of structural materials, because of its superior properties of strength, toughness, hardness and corrosion. In recent years, its superior strength, hardness and corrosion resistance have been particularly noted, and as a result, the sintered body of zirconia has been extensively used for a ferrule, which is a part of an optical fiber connector. Among sintered body of zirconia, those comprising fine grain have superior above-mentioned properties, and therefore, it is desired to obtain fine-particle zirconia powder having a primary particle diameter of not more than 0.1 μm.
As a process for producing fine zirconia powder, for example, JP-A5-24841 discloses a process consisting of the steps of:
(1) dissolving zirconium oxychloride in water to obtain a solution,
(2) heating the solution and hydrolyzing zirconium oxychloride therein to precipitate zirconia hydrate,
(3) drying the precipitated zirconia hydrate, and
(4) calcining the dried zirconia hydrate at 850° C. to obtain zirconia powder having a primary particle diameter of not more than 0.1 μm.
However, the above-mentioned process has a problem that a reaction rate of the hydrolysis in the step (2) is so slow that it takes as long as 80 hours until the hydrolysis reaches 84%.